22 



OSTEOLOGY. 



The notches are excavations in the anterior and posterior sur- 

 faces of each pedicle, so placed that when the vertebras are in situ 

 the botch in the posterior part of one pedicle corresponds with 

 that in the anterior of the next, the two forming a large opening, 

 called the intervertebral foramen, which leads to the neural 

 canal and gives passage to the spinal nerve and blood-vessels. 



Each true vertebra, with the exception of the two anterior 

 cervical ones, has four oblique or aHicular processes (zyga- 

 pophyses) on the superior and lateral parts of the arch. The 

 faces of the anterior of these processes are directed upwards and 

 inwards, those of the posterior downwards and outwards ; as 

 their name implies, they articulate and form joints with the 

 corresponding processes of contiguous vertebrae. In some of the 

 dorsal and lumbar segments of certain animals, the anterior 

 zygapophyses have processes which project above the level of the 

 articular facets; these are the mammillary processes (meta- 

 pephyses). 



The transverse processes (diapophyses), one on each side, 

 spring from the sides of the body and pedicle, and are projec- 

 tions varying much in size and shape in 

 the different regions. Between the anterior 

 zygapophysis and the metapophysis in some 

 animals there may be another small emin- 

 ence projecting backwards (anapophysis). 



The spinous processes are superior and 

 inferior. The superior or neural spine 

 (neurapophysis), formed by the union of the 

 laminee, and surmounting the centre of 

 the arch, is sometimes of great size and 

 strength, but varies much in development 

 in the different regions of the same animal. 

 The inferior (hypapophyses) are for the 

 most part rudimentary, and can scarcely be 

 said to exist, except in the cervical region, 

 where they project from the inferior central 

 line of the bodies. 



The centra or bodies of the vertebrae, 

 placed in natural apposition, thus form a 

 central bony column, to which the arches 

 and processes are attached ; the arches, with their connecting 

 ligaments, form superiorly a cavity, the spinal or neural canal. 



'^^.f^ 



Fig. 7. 



Diagramatic transverse sec- 

 tion from the skeleton of a 

 mammalian thoiax, showius 

 the chief features of a perfect 

 vertebral segment. 1, Neural 

 spine, 2,Lamina(neurapophy- 

 sis); 3, Pedicle; 4, Neural arch; 

 5. centrum; 6, Inferior Spine 

 (hypapophysis) : 7 7, Haemal 

 arch ; 8,Rib(pleurapophysis); 

 9, Costal cartilage (haema- 

 pophysis) ; 10, Sternebra . 

 11, Hseraal spine. 



